Question

I am using Ruby on Rails 3.2 and I would like to know if there is a way to make the following:

@categories.order('user_id = ? DESC', params[:id])
@categories.order('user_id = ? DESC', @user.id)

# Note: It is almost the same as `@categories.where('user_id = ?', params[:id])`
# but for the `order` clause.

Above statements generates this error:

ActiveRecord::StatementInvalid (Mysql2::Error: You have an error in your SQL 
syntax; check the manual that corresponds to your MySQL server version for the 
right syntax to use near '? DESC, ...

Answer 1

If you are trying to change the order based on the user_id, returning those that match first, you should be using a CASE statement.

In raw SQL, it would look like this:

SELECT * FROM Categories ORDER BY CASE user_id WHEN 34 THEN 1 ELSE 2 END

That would bring all of rows where user_id is 34 to the top, leaving the rest to default ordering.

Now, like others have mentioned, order does not have any mechanism to sanitize SQL, so you will have to use the protected class method on ActiveRecord::Base.

It may look like this:

order_sql = Category.send :sanitize_sql_array, ["CASE user_id WHEN ? THEN 1 ELSE 2 END", some_user_id]

@categories.order(order_sql)